From 53ed3d91a141f5c8b3bce45b0004fbbfefe77956 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Mon, 5 Jan 2026 10:02:32 +0100 Subject: [PATCH] x86/segment: Use MOVL when reading segment registers Use MOVL when reading segment registers to avoid 0x66 operand-size override insn prefix. The segment value is always 16-bit and gets zero-extended to the full 32-bit size. Example: 4e4: 66 8c c0 mov %es,%ax 4e7: 66 89 83 80 0b 00 00 mov %ax,0xb80(%rbx) 4e4: 8c c0 mov %es,%eax 4e6: 66 89 83 80 0b 00 00 mov %ax,0xb80(%rbx) Also, use the %k0 modifier which generates the SImode (signed integer) register name for the target register. [ bp: Extend and clarify commit message. ] Signed-off-by: Uros Bizjak Signed-off-by: Borislav Petkov (AMD) Reviewed-by: H. Peter Anvin (Intel) Tested-by: Michael Kelley Link: https://patch.msgid.link/20260105090422.6243-1-ubizjak@gmail.com --- arch/x86/include/asm/segment.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h index f59ae7186940a..9f5be2bbd2918 100644 --- a/arch/x86/include/asm/segment.h +++ b/arch/x86/include/asm/segment.h @@ -348,7 +348,7 @@ static inline void __loadsegment_fs(unsigned short value) * Save a segment register away: */ #define savesegment(seg, value) \ - asm("mov %%" #seg ",%0":"=r" (value) : : "memory") + asm("movl %%" #seg ",%k0" : "=r" (value) : : "memory") #endif /* !__ASSEMBLER__ */ #endif /* __KERNEL__ */ -- 2.47.3